83 Vanagon bucking at 60 mph

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83AC
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83 Vanagon bucking at 60 mph

Post by 83AC » Wed Mar 02, 2016 2:44 pm

Hey there fellow Vanagon owners! This is my first post here, or in any of the forums. Our 83 Vanagon has been starting to buck and lose power if I continue to try to accelerate when it reaches about 60mph. It does this consistently and has been since about the end of the summer (haven't done too much winter driving). When we first got Penny Lane, she drove at 65 to 70 steady no problem. When going downhill, she speeds right up past 60 to 65/70 no problem, and can sometimes hold that for a bit on flat ground if the wind isn't in our face, but really once the momentum of the hill is gone, the bucking comes back right around 60mph.

The only other time I have replicated the problem in a different gear is driving up steeper inclines in 3rd gear and trying to get above 40-45, or 30-35 depending on said incline. However, this was prior to the bucking starting on flat ground around 60mph. The mechanic who inspected Penny when we bought her informed me that this bucking had been an issue they had not been able to figure out after weeks of exploration in the shop. Just so it's out there, she was a CA van in her previous life and they thought maybe it had to do with a relay in the emissions equipment from CA. As an additional note, mpg has dropped from a pretty consist 17-19 on the highway and through hills to somewhere around 11-13.

As far as diagnosis, I'm pretty new to understanding engines and mechanics, so bear with me here. Listening to the engine, it does sound like I have a vacuum leak (hissing), seems to be near the distributor, but I could be wrong. I've replaced the idle retard vacuum hose, which did seem to lower the rpm at idle. I need to find where the vacuum leak(s) is/are, and I'm nervous about spraying anything flammable near that spot without someone experienced with me :bom: . Anyone want to help?

This past summer another vanagon owner helped me out some and identified through looking at spark plugs that it was running lean. We also checked the timing and it was looking good. I adjusted the gear in the AFM about 5 clicks counter clockwise to richen the mixture, but haven't done any further checking of spark plugs yet, and I didn't adjust anything else at that time.

I'm not positive when the fuel filter was last replaced. It's been suggested that I replace that as a start to see if it fixes the bucking. I'm going to order one of those this week.

Alright - into the rabbit hole I go! Hopefully, with your extensive banks of knowledge and guidance, I will be successful in learning :salute:
Say what you mean; do what you say.
1983 AC Vanagon camper - Penny Lane

cegammel
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Re: 83 Vanagon bucking at 60 mph

Post by cegammel » Wed Mar 02, 2016 5:06 pm

If it makes you feel better, my 1980 cruises beautifully up to 62...at 65, my head temps climb into the 375-390 range, and I back it down. I've never seen 70, except downhill... I have experienced some unexplained bucking under a too heavy foot in too high a gear...

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Randy in Maine
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Re: 83 Vanagon bucking at 60 mph

Post by Randy in Maine » Wed Mar 02, 2016 5:26 pm

Change out the fuel filter for $7 and then have a look at the TS II for $20.
79 VW Bus

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Amskeptic
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Re: 83 Vanagon bucking at 60 mph

Post by Amskeptic » Wed Mar 02, 2016 7:33 pm

cegammel wrote: 65, my head temps climb into the 375-390 range, and I back it down.
Why do you back off at such low temperatures? I would never get across the country if I backed off below 400-420*.
Colin

(p.s. the bucking in your example with Penny Lane would likely be too rich if 11-13 mpg is current consumption. If the AFM has not been monkeyed with, it would suggest checking the TS 2 as RandyInMaine suggested)
BobD - 78 Bus . . . 112,660 miles
Chloe - 70 bus . . . 206,845 miles
Naranja - 77 Westy . . . 116,898 miles
Pluck - 1973 Squareback . . . . . . 55,570 miles
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83AC
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Re: 83 Vanagon bucking at 60 mph

Post by 83AC » Wed Mar 02, 2016 8:01 pm

Would it be wise to turn the AFM clockwise a few turns and see if the bucking goes away first? Then check for vacuum leaks and the TS2? Or better to leave the AFM and first look to the TS2?

On a drive this evening, going uphill in 3rd, it didn't buck until I hit 40-45. Backing off fixed that. On the highway, pretty much same situation with the bucking around 60-62 on flat, lower on uphill. Though there was one stretch where I could hold 65 no problem and no bucking, but maybe that was a fluke. It seems that only near the top end of the mph range for gears does it do this behavior.
Say what you mean; do what you say.
1983 AC Vanagon camper - Penny Lane

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Re: 83 Vanagon bucking at 60 mph

Post by Amskeptic » Thu Mar 03, 2016 7:51 am

83AC wrote:Would it be wise to turn the AFM clockwise a few turns and see if the bucking goes away first? Then check for vacuum leaks and the TS2? Or better to leave the AFM and first look to the TS2?

On a drive this evening, going uphill in 3rd, it didn't buck until I hit 40-45. Backing off fixed that. On the highway, pretty much same situation with the bucking around 60-62 on flat, lower on uphill. Though there was one stretch where I could hold 65 no problem and no bucking, but maybe that was a fluke. It seems that only near the top end of the mph range for gears does it do this behavior.
In this case, there is no real serial methodology to your diagnosis. Keep your mind open.

Imagine that bucking at the "top end in each gear" just means that the engine is starving for fuel. You would change the fuel filter and saw the old one open to see if there is rust that might be the cause.

If you are getting only 11-13 mpg, then bucking at higher rpm suggests an ultra rich fuel mixture or air starvation. Yiou would inspect the air filter make sure it is clean, and you would adjust the AFM leaner (at a fully warmed up idle, you would turn the screw CLOCKWISE first, to see if the idle improves as you richen, find highest rpm, then counterclockwise LEAN for a 25 rpm drop into the lean zone, yer done).

If you are getting ignition breakdown at high rpm, you would check all resistances in spark plug connectors, rotor, and check for damaged spark plug insulation especially if near metal or if the wire cross each other tightly.

If it is too intermittent to narrow down specifically, just change out that TS 2, it can make life miserable in the realm of intermittent misbehavior.
Colin
BobD - 78 Bus . . . 112,660 miles
Chloe - 70 bus . . . 206,845 miles
Naranja - 77 Westy . . . 116,898 miles
Pluck - 1973 Squareback . . . . . . 55,570 miles
Alexus - 91 Lexus LS400 . . . 84,465 miles

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Re: 83 Vanagon bucking at 60 mph

Post by reluctantartist » Mon Mar 07, 2016 5:04 pm

I will be posting here soon about my on going mpg problem.....but I also had issues similar to yours, I was able to go above 60 but I had to do it gradually. If I floored it, it would buck. It ended up being the ECU. Get the L-jet manual and a digital volt ohm meter. Pull the ecu plug and start checking what is going on. Your grounds probably have high resistance and from the plug you can also check the temp2 and the temp 1 in the AFM . You will also want to check the continuity of wiring to the full throttle switch i(I had to replace the connectors on that as well due to corrosion in the connection which caused high resistance). I even had high resistance in the temp2 wire connection and had to replace that connector as well. Get a vacuum gauge and check it. Is this a cal l-jet or federal? If it is a California ignore the full throttle check in the manual on the ecu plug. That is only for a federal ignition. Also make sure the connection at the starter is corrosion free and tight.
82 Westy

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SlowLane
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Re: 83 Vanagon bucking at 60 mph

Post by SlowLane » Tue Mar 08, 2016 8:20 am

I had bucking identical to yours about eleven years ago. Eventually tracked it down to a leaking AAR elbow. The elbow looked fine from a casual inspection until I actually took it out, then it was obvious. The leak was on the underside where I couldn't see. Problem recurred just a couple of months later. "Can't be that elbow", I reasoned, "I just replaced it." But sure enough, the crappy aftermarket elbow had split right apart. Replaced with a genuine VW part and all was good again.

Eradicate vacuum leaks and electrical issues first before fiddling with the AFM, especially if yours is a CA model, because the lambda-feedback loop will fight you with every AFM adjustment you make. With a CA model, the vacuum retard can is another potential source of vacuum leaks.
'81 Canadian Westfalia (2.0L, manual), now Californiated

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energyturtle
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Re: 83 Vanagon bucking at 60 mph

Post by energyturtle » Tue Mar 08, 2016 9:15 am

I've had this issue numerous times. First fuel filter, second check all grounds, especially the three prong connection under the plenum. 99% of the time bucking is related to fuel starvation, or intermittent loss of ground breaking the circuit to the ignition system, and or c.p.u. Third, I would look into vacuum. Let's us know how it goes. For now I would leave the AFM alone, as not to add to the issue

Scottie

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Re: 83 Vanagon bucking at 60 mph

Post by 83AC » Sat Mar 19, 2016 7:35 pm

Update:
Today we replaced the fuel filter and connecting hoses. After replacing it, I cut the old one open - no rust. Also, the other evening I turned the AFM clockwise about 3 cogs to correct back toward where it started - I had initially turned it counterclockwise about 4 or 5 cogs because it was running lean (mistakenly didn't mark original location). Went for a highway drive up to 65mph. Bucking returned, always right at 60mph. It was not as constant this time, and depending on wind direction, there were times that we cruised at 65 on flat or slight uphill no problem. So some slight improvement.

Later I checked the distributor cap and rotor and am wondering if it needs replacing. Last knowledge of it being replaced was by PO in about 2010/11. End of rotor looked burned/blacked and the points in the cap looked worn. Since it only happens under higher RPM and seems to have gotten worse, maybe this is an issue? I then replaced the idle advance vacuum tube also since the old one looked beat.

I went for another drive and had similar experience. Into the wind, anything over 60 bucks. With the wind or behind a truck, 65 to 70 seems good. Filled the tank, combined gas mileage was 9.7mpg - continues to get lower. I have had it idling a lot.

Any further thoughts?
Say what you mean; do what you say.
1983 AC Vanagon camper - Penny Lane

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SlowLane
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Re: 83 Vanagon bucking at 60 mph

Post by SlowLane » Tue Mar 22, 2016 10:16 am

83AC wrote:Any further thoughts?
Yes. Book an appointment with Colin.
'81 Canadian Westfalia (2.0L, manual), now Californiated

"They say a little knowledge is a dangerous thing, but it is not one half so bad as a lot of ignorance."
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Re: 83 Vanagon bucking at 60 mph

Post by energyturtle » Tue Mar 22, 2016 6:10 pm

Excuse me if this has already been mentioned. Are you still running EGR and other emissions devices? Correct me if I'm wrong, but about the time EGR is opened under higher RPM's, isn't that where your power loss is occurring?
Scottie :scratch:

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Randy in Maine
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Re: 83 Vanagon bucking at 60 mph

Post by Randy in Maine » Wed Mar 23, 2016 6:21 pm

Did I miss the part where you checked the Temp Sensor II?
79 VW Bus

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Amskeptic
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Re: 83 Vanagon bucking at 60 mph

Post by Amskeptic » Wed Mar 23, 2016 6:24 pm

Randy in Maine wrote:Did I miss the part where you checked the Temp Sensor II?
Randy!
You have to report your business affiliation with Temp Sensor II, INC, each time you plug it.
We have discussed this.
Colin
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BobD - 78 Bus . . . 112,660 miles
Chloe - 70 bus . . . 206,845 miles
Naranja - 77 Westy . . . 116,898 miles
Pluck - 1973 Squareback . . . . . . 55,570 miles
Alexus - 91 Lexus LS400 . . . 84,465 miles

83AC
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Re: 83 Vanagon bucking at 60 mph

Post by 83AC » Wed Mar 23, 2016 8:13 pm

energyturtle wrote:Excuse me if this has already been mentioned. Are you still running EGR and other emissions devices? Correct me if I'm wrong, but about the time EGR is opened under higher RPM's, isn't that where your power loss is occurring?
Scottie :scratch:
The EGR is no longer on this van. The tubes that connected it are crimped closed - I didn't ever know what those were.

As for the temp sensor I I, I think I finally made sense of where it is and now can move on to test it. I was feeling pretty confused about testing things and then realized I have to have the ignition in "on," correct?

I looked at the spark plugs and checked the distributor cap and rotor. Plugs look like things are lean or too hot. Cap and rotor are in good shape. I looked at grounds - a little confused because I thought there was supposed to be a wide ground strap somewhere in the engine compartment of my 83AC and I can't find one - the grounds are definitely dirty and need cleaning.
Say what you mean; do what you say.
1983 AC Vanagon camper - Penny Lane

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